After 10 years and a journey of 4 billion miles, the European Space Agency’s Rosetta spacecraft
arrived at its destination yesterday for the first extended, close examination of a comet.

A six-minute thruster firing at 5 a.m. Eastern time, the last in a series of 10 over the past
few months, slowed Rosetta to the pace of a person walking, about 2 mph relative to the speed of
its target, Comet 67P/Churyumov-Gerasimenk.

“It is like driving a car or a bus on a motorway for 10 years,” said Andrea Accomazzo, the
flight director, at a post-rendezvous news conference. “Now, we’ve entered downtown. We’re downtown
and we have to start orienting ourselves. We don’t know the town yet, so we have to discover it
first.”

Over the coming months, Rosetta and its comet, called C-G for short, will plunge together toward
the sun. In November, a small 220-pound lander is to leave the spacecraft, set down on the comet
and harpoon itself to the surface, the first time a spacecraft will land gently on a comet.

At this point, the comet and its shadowing spacecraft are more than 330 million miles from the
sun (more than three times as far out as Earth), traveling at 35,000 mph.

With the final firing of the thruster, Rosetta was a mere 60 miles from the comet’s surface.

“This morning, we hit a milestone, an important milestone of this mission,” said Laurence O’R
ourke, a member of its science team.

“But this mission isn’t just about arriving at a comet,” he went on. “It’s about studying the
comet. It’s about placing a lander on a comet, but again, the mission does not end there. The
science continues. We’re trying to follow this comet all around its orbit.”

Rosetta is still not close enough to be captured by the comet’s gravity but instead will be
flying a triangular path in front of the comet as it maps the surface. It eventually will move
within 6.2 miles of the surface and enter orbit around the comet.

Comets, made of ice, dust and rock, are frozen leftovers from the formation of the solar
system.